So the rear spoiler was one of the first mods I did when restoring the car, and to be honest I made a few mistakes while doing it. At the time the only spoiler available was made from a heavy rubber type stuff, which I bought and made a mould of because the rubber couldn't be smoothed into the body as I wanted, but not knowing a huge amount about moulding at the time it wasn't the best cast ever, and took a bit of cleaning up. I also used the wrong resin, which was far too hard, and more recently I had noticed a few cracks around where it joined to the body, so came up with a cunning plan for a one off roof job.
The next job was to check for signs of rust and give it a good going over with a small straight wire brush in a dremel as with rust its best to get right back to clean metal to be sure it's gone.
I then gave it a coat of por 15 anti rust paint which I had read great things about, then when dry as odd as it seems sanded it back leaving only paint in the pitted areas, and the rest clean bare metal. The reason for this is I am going to smooth the roof off to the outer edge of the gutter and to do this the edge needs filling and smoothing over, a job for high density pu foam, which sticks so much better to bare metal than paint.
The foam is a two part liquid oppose to the low density you get in a aerosol can, as when the two part is mixed, its just like water so can be poured into the gutter and it gets into every nook and cranny, prior to expanding. When cured I poured another lot on top of that to get the angle I wanted then with a bread knife cut off the access to leave me with the smoothed edge.
The next job is to apply filler, but not that crappy stuff you buy in car shops, as its way to thick and sets in the blink of an eye and tends to delaminate over time if applied in layers. I am using epoxy resin mixed with talc which is a filler, that way I can make it the consistency I need.
The first layer is runny as it needs to fill and soak into the surface of the pu foam to be a good base, plus with a 90 minute curing time it allows you to really work it in.
The following coats are much thicker as in almost paste like consistency and applied with a metal spatula and quite liberally, as they will be sanded back smooth when hard.
Now when finished the roof will be skinned with carbon fibre, so the first job is to place strips along the edges so when done the whole roof will form a sort of roof cap.
This is quite fiddly as the carbon has to be put on then wrapped under the gutter and held there, but luckily you can get different viscosities of epoxy so a thick one also acts more glue like which allows you to paint it on, then fold the carbon over, then cover with a film and tape in place.
Yes it's kind of fiddly, but by taking the carbon under the gutter will form a water tight finish, then when I fillet the edge to form a drip strip there will be no chance of anything cracking over time and letting water in.
However I decided for it to look properly done it would have to go on before the roof was skinned in carbon fibre or there would be a join, instead of looking like just one proper moulding, so I cut it out in several parts on my router then took the plunge and stuck it on.
Its cut from high density pu foam block, as this is solid but light and flexible enough to fit the curve of the roof. The first job was to mark the roof out to get it central as how bad would it look wonky and off centre. Once happy with its placement small recesses were cut out of the edges and wooden blocks temporally glued to the roof to make lining it up when covered in epoxy much easier.
To get it stuck to the exact curve and shape of the roof it was going to need vacuum bagging direct to the roof of the car, so I set about making one to fit. This involves taping special film over the roof which stretches, then inserting a air out port which is connected to the vacuum pump, then cut a piece of breather felt to go from the outlet port to the foam shape, so it can draw all the air out sucking the film and foam part tightly down onto the roof. I then did a trial run and found it pulled down nicely so as it was a really hot day, mixed the epoxy and spread it over the bottom of the foam shape and put it in place, then connected everything up.
Three hours later, (it does only take ninety minutes to cure, but I decided to leave it longer as better safe than not stuck down,) then removed all the vacuum bagging stuff and it was stuck.
I then spent a couple of hours hand finishing it so it flowed evenly once on the roof and feathered out towards the edge, not something I could add to the router program as it needed that hand touch to fit perfectly.
This is an ongoing project along with a couple of others so check back
from time to time to see how its progressing.